This invention relates in general to the construction of coke ovens and, in particular, to a new and useful method of operating the sprinkling system of a coke oven flue, which includes collecting the condensate of a sprinkling liquid from the flue along with tar, tar oils, hydrocarbons and ammonia, and directing it into a separator to separate out a sprinkling liquid from the condensate and returning the sprinkling liquid to the condensate along with a tar free of solids, at least during an initial period of operation of the coking oven.